Straight line motor control for an x-y plotter



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STRAIGHT LINE. MOTOR CONTROL FOR AN X-Y PLOTTER Filed Dec. 29, 1961 19 Sheets-Sheet 1 William J. Muldoon, Robert W. Peterson,

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CONTROL FOR AN X-Y PLOTTER STRAIGHT LINE MOTOR Sheets-Sheet 1 Filed Dec. 29, 1961 Feb. 13, 1968 R. w. PETERSON ETAL 3,359,163

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CONTROL FOR AN )("Y PLOTTER 9 Sheet$Sheet 1 1 STRAIGHT LINE MOTOh Feb. 13, 1968 Filed Dec. 29, 1961 Feb. 13, 1968 STRAIGHT LINE MOTOR CONTROL FOR AN X Filed Dec. 29, 1961 R. W. PETERSON ETAL *1' PLOTTER g Sheets-Sheet 1L R. w. PETERSON ETAL 3,369,163

CONTROL FOR AN X-Y PLOTTER l9 Sheets-Sheet 1v Feb. 13, 1968 STRAIGHT LINE MOTOR Filed Dec. 29, 1961 F 1968 R. w. PETERSON ETAL 3,369,163

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STRAIGHT LINE MOTOR CONTROL FOR AN X-Y PLOTTER 19 Sheets-Sheet 19 Filed Dec. 29, 1961 United States Patent 3,369,163 STRAIGHT LINE MOTOR CONTROL FOR AN X-Y PLOITER Robert W. Peterson, Sepulveda, and William J. Muldoon,

Palos Verdes Estates, Calif., assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Dec. 29, 1961, Ser. No. 163,340 8 Claims. (Cl. 318-162) This invention relates generally to systems of electrical control, and more particularly to such systems which are capable of accurately positioning and moving an element in accordance with a predetermined instruction program.

While the descriptive disclosure hereinafter is particularly directed to a system for moving a pen or other line drawing implement according to a specified program for the purpose of making drawings, writing, printing and the like, it will be appreciated that this invention is not particularly limited to such a specific function or to such a particular type of output device but may be used to power any suitable device in the layout or manufacture of printed circuits in machining operations, etc.

Efforts have been made by others to automatize drafting, that is, to automatize the making of line drawings. These prior art systems have been developed to the point where the specific drawing is completely encoded on a digital record member as a digital program. These systems are usually based upon a system of mathematics, defining straight lines in point-slope form. The digital program is transduced in a specific sequence and converted to analog form to power a suitable type of analog servo system having a pair of servo motors which power and move a single output member in each of two mutually perpendicular directions.

These prior art arrangements have proved satisfactory for drawing straight lines at differing slopes. They are, however, usually complicated in the use of velocity servos in providing a line generating output member so that output speeds of long lengths of lines do not exceed predetermined maximum values beyond which the line generating operation becomes uncertain. For instance, if an ink pen is used as the line drawing implement the upper servo speed is determined by the upper limit of pen speed at which ink can be satisfactorily deposited. The rate of change of servo speed also presents a problem in such arrangements and requires special precautions to avoid excessive acceleration in both accelerating and deceleratin g modes.

An object of this invention is to provide an improved system for generating straight lines of any slope.

A further object of this invention is to provide an improved system for generating straight lines in which the position of the line in a reference plane, such as a drawing board, is defined in terms of rectangular coordinates from a fixed point of reference to the geometric center of the straight line.

It is also an object of this invention to provide an improved system for generating straight lines in which the lines are defined in two coordinates with respect to their geometric centers.

More particularly, it is an object hereof to provide an improved system for generating straight lines in which provision is made for completely defining the line in a reference plane in terms of distances in two coordinates from a reference point in the reference plane to the geometric center of the straight line, together with distances in two coordinates defining the starting point of the line.

Still another object of this invention is to provide an improved system for generating geometric figures which includes provisions for simultaneously generating cosine voltages for controlling position servos.

3,369,163 Patented Feb. 13, 1968 It is additionally an object of this invention to provide an improved electrical control system including provisions for generating respective cosine voltages having ampliludes determined by the coordinates of the starting point of a line with respect to its geometric center and steady state voltages indicating the center of a line and for algebraically combining these differing quantities in differing ways to produce an electrical quantity having a desired time varying characteristic.

A specific object of this invention is to utilize cosine varying voltages in controlling the motors of an X-Y type of position servo system for describing or generating straight lines.

The aforesaid and other objects and advantages are achieved in an arrangement according to this invention which generates and employs time variable electrical quantities characterized by selected time parametric functions for controlling a servo system to selectively describe straight lines, circular arcs, or circles, and elliptical arcs, or ellipses, of specific dimension or sizes and at particularly defined points in a given reference plane, such as a drawing board.

The program of the servo system is digitally encoded on a suitable record medium, such as paper tape. magnetic tape or other record bearing medium, as a discrete information code system in conventional binary code, for instance, together with other discrete information recordings having place of position significance on the medium for directing control of specific control elements in the system. Suitable transducers read this medium or tape and the signals thus generated after suitable conversion, amplification and shaping, if needed, are stored in a digital storage circuit such as a shift register which may include a plurality of flip flops conventionally set in correspondence with the respective discrete signals. The digitally encoded information includes the following:

(1) Dimensions in both coordinates from a reference point in the reference plane to the geometric center of the figure which is to be drawn.

(2) Dimensions and their signs defining the starting point of any line describing a geometric figure in terms of respective coordinates of that oint referred to the geometric center of the figure.

(3) Dimensions and their signs defining the stopping point of any line.

(4) Respective commands denoting if a circular are or any ellipse is to be drawn.

(5) Respective commands denoting which of several line thicknesses is to be used.

(6) Respective commands denoting if any of several line interruption patterns (line characteristics) is to be used.

The system includes a variable frequency electrical function generator for generating sine and cosine electrical quantities of a fixed magnitude which are relatively positive or negative depending upon the algebraic signs of the coordinates defining the starting point of the line describing the geometric figure in relation to the geometric center of the figure and which vary in frequency as a function of a selected algebraic combination of at least a portion of the information defining these coordinates to provide time varying output voltages having a frequency roughly inversely proportional to the desired length of a line.

The time varying voltages thus generated are attenuated. or amplitude modulated, or multiplied by another voltage, or otherwise suitably modified, in selected pairs as a function of the coordinates of the starting point of the line defining the figure to provide simultaneous time varying X and Y line generating voltages, the corresponding instantaneous magnitudes of which jointly define respective points on the line describing the figure. 

1. A LINE GENERATING SYSTEM, COMPRISING: A PAIR OF SERVOS HAVING RESPECTIVE INPUT CIRCUITS AND HAVING RESPECTIVE OUTPUT MOTORS; A DEVICE HAVING A PAIR OF INPUT MEMBERS CONNECTED TO AND DRIVEN BY SAID MOTORS, RESPECTIVELY, AND HAVING A MOVABLE LINE GENERATING OUTPUT MEMBER CONNECTED TO AND DRIVEN BY BOTH OF SAID INPUT MEMBERS IN SUBSTANTIALLY MUTUALLY PERPENDICULAR DIRECTIONS; MEANS, INCLUDING AN OSCILLATOR FOR PRODUCING A COSINE VOLTAGE HAVING A LINE GENERATING COSINE VOLTAGE OUTPUT CIRCUIT; MEANS CONNECTING SAID LINE GENERATING COSINE VOLTAGE OUTPUT CIRCUIT TO ONE OF SAID SERVO INPUT CIRCUITS; AND MEANS CONNECTING SAID LINE GENERATING COSINE VOLTAGE OUTPUT CIRCUIT TO THE OTHER OF SAID SERVO INPUT CIRCUITS. 